Jack connector

The jack connector, also sometimes called a TRS (tip, ring, sleeve) connector is commonly used for analog signals including audio. It was invented for use in telephone switchboards in the 19th century and originally was of a 1/4" (6.35 mm) diameter. These days it is also available with other dimensions, most widely with a 3.5mm (approx. 1/8") diameter. Signal wires require shielding, usually by the ground wire forming a sleeve around the insulated signal wire. Conventionally the signal wire goes to the tip and the shield or ground wire to the sleeve.